Telematics Chapter 2 The Internet as a Blackbox: Terminology &
Concepts
Dr. habil. Emmanuel Baccelli
INRIA / Freie Universität Berlin
Institute of Computer Science
2.2
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.3
2.4
Simplex Channel Half-Duplex Channel
Duplex Channel
Dedicated Ressources
Sharing resources saves costs: By communication, one can access
resources of other parties Several institutions can share expensive
resources Requirements: Efficient mechanisms for data exchange
between components of a distributed system Efficient mechanisms to
minimize blocking due to multiplexing
The “driving power” for the enormous increase of data
communication: Decreasing costs for hardware…
… while the computing power increases. Jevons paradox
2.10
Circuit Switching vs. Packet Switching
Circuit switching establishes dynamically a dedicated communication
channel before communication starts Explicit communication channel
=> transmitted data don’t need to carry addresses Provides full
bandwidth of the channel to the parties Disadvantages? What happens
with the reserved resources during silence?
Circuit Switching
Circuit Switching vs. Packet Switching
Packet switching allows parallel sharing of the same resource for
different communication endpoints Overhead: Transmitted data need
to carry address Buffers introduce variable delay but are required.
Why? More: L. G. Roberts: “The Evolution of Packet Switching”,
Proc. of IEEE, 66(11), 1978.
Packet Switching
2.12
IP Address
receive(port)
Internet
API
• Port numbers are coded on 16 bits, from 0 to 65535 • IPv4
addresses are coded on 32 bits, represented as four octets
A.B.C.D
2.13
The Internet as a Bit Delivery Service
• Port numbers are coded on 16 bits, from 0 to 65535 • IPv6
addresses are coded on 128 bits, represented in colon hex
notation
Internet
2.14
receive(port)
Port allows application multiplexing on a single host Application
Programming Interface (API) allows developers to
access other services
2.15
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.16
Virtual Pipe (Internet)
Data (File, Stream…)
Digital Data Communication = processing and transport of digital
data between interconnected computers
2.17
The Term of Data
An apple can be represented by: The word “apple” The drawing of an
apple etc.
A definition for “data”: Representation of facts,
concepts, and statements in a formal way which is suitable for
communication, interpretation, and processing by human beings or
technical means.
Examples for data representation Spoken language Sign language
Written language
Representation in a formal way
Conventions for the representation of objects of thought.
Objects of thought Facts, Concepts,
Ideas, Models, etc.
2.19
The Term of Information
Generally, information is whatever is capable of causing a human
mind to change its opinion about the current state of the real
world. Formally, and especially in science and engineering,
information is whatever contributes to a reduction in the
uncertainty of the state of a system; in this case, uncertainty is
usually expressed in an objectively measurable form.
(Oxford Reference Online)
The communication or reception of knowledge or intelligence
Information has to be distinguished from any medium that is capable
of carrying it
Humans and machines can handle data, however only humans can handle
information
2.20
The Term of Signal
A signal is the physical representation of data by spatial or
timely variation of physical characteristics The variable parameter
that
contains information and by which information is transmitted in an
electronic system or circuit. The signal is often a voltage
source in which the amplitude, frequency, and waveform can be
varied.
Signal is the real physical representation of an abstract
representation
abstract World
physical World
Objects of thought Facts, Concepts, …
Signals as real representation of data
Conventions for the representation of data
2.21
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.22
What is a Protocol?
Human protocols: “What’s the time?” “I have a question”
Introductions
In General … specific messages sent … specific actions taken
when
messages received or other events happen
Network protocols: Machines rather than humans All communication
activities in the
Internet is governed by protocols
In General Protocols define format, order of
messages sent and received among network entities, and actions
taken on message transmission and receipt
2.23
To enable understanding in communication, all communication
partners have to speak the same “language”.
§ Types of message §Syntax of messages §Semantics of messages
§When/how to send a message §When/how to respond to a message
§Control/multiplexing over media access § Priorities §Handling of
transmission errors §Sequence control / Fragmentation §…
Why Protocols?
Protocol A protocol is a set of unambiguous specifications defining
how processes communicate with one another through a connection
(wire, radio etc.).
2.25
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.26
Need for quantitative, measurable parameters, such as:
Technical Performance Required transmission performance, delay,
jitter, throughput, data rate, etc.
Costs Investment costs, cost of operation, etc.
Reliability Fault tolerance, system stability, immunity,
availability, 99999
Security and Protection Eavesdropping, authentication, denial of
service, etc.
Dedicated term in the tech lingo: QoS (Quality of Service) ITU
standard Recommendation ITU-T E.800: definition of terms related to
QoS
2.27
(One-way) Delay Measured in seconds [s] d1 = t‘1 – t1
Round-trip-time (RTT) Measured in seconds [s] r1 = t2 – t1
RTT should also integrate the processing time in B Usually
negligeable compared to
delay
Jitter: fluctuation between successive arrivals Measured in seconds
[s] First calculate delay as
d1 = t‘1 – t1
d2 = t‘2 – t2
di = t‘i – ti
j2 = d3 – d2
ji = di+1 – di
Irregular arrivals are difficult to deal with. e.g. need to buffer
before start of video
stream, to playback at constant speed. Optimal buffer size?
A B
Goodput useful throughput from the user
perspective (i.e. throughput minus control traffic overhead).
Do not use „bandwidth“ as a synonym for throughput!!
A B
t‘3
t‘4
data1 = b1 bits data2 = b2 bits data3 = b3 bits data4 = b4
bits
t data
T i
Bit sent
t Delay in seconds
Bit received (virtual) pipe
Example: Store capacity of the transmission line § With a
connection of 1 Mbps, 200 ms delay: 1 Mbps × 0.2 s = 200 kbit §
With a connection of 100 Mbps, 100 ms: 100 Mbps × 0.1 s = 10
Mbit
2.31
Passive: Eavesdropping
S D
QoS: More Basic Aspects
Packet loss rate What guarantees for the bit delivery service?
Best-effort? More?
Bit error rate ‘Finer-grained’ caracteristic for the bit delivery
service
2.33
QoS requirements may impact the choice of communication
architecture
Example 1 You want to increase the availability of a service. Which
architecture will be the cheapest to achieve that? Example 2 You
want to offer online storage service. What are the alternatives in
terms of architecture?
2.34
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.35
Advantages of the Client/Server Principle § Cost reduction § Better
usage of resources §Modular extensions §Reliability by
redundancy
2.36
Server! Program (process) which offers a service over a
network.
Servers receive requests and return a result to the inquiring
party. The services offered include simple operations (e.g. name
server) or a complex set of operations (e.g. web server).#
Client# Program (process) which uses a service offered by a
server.
Examples for Client/Server Systems
Client Server Web Browser Web Server E-Mail Program Domain Name
System (DNS) FTP Client FTP Server
2.37
Contents
The Big Picture: Internet as a Bit Delivery Service Virtual
Pipe
Basic Terminology Data vs. Information vs. Signal Communication
Protocol
Basic Concepts Evaluation Communication Quality Client-Server
Architecture Peer-to-Peer Architecture
2.38
Serverless Resource Sharing: Peer-to-Peer
The Peer-to-Peer (P2P) concept: No fixed client and server roles
Direct connections between any pair of computers
2.39
P2P
Advantages No expensive servers No central point of failure No
central point of control
Drawbacks Everyone needs to dedicate ressources Somewhat more
complex
Examples Using the P2P Paradigm § BitTorrent (filesharing) § Skype,
SIP § Ad-Hoc Networks, Spontaneous Wireless Networks § Some
botnets
2.40
Unicast: Two peers communicate.
Broadcast: One sender transmits to all other peers in the
network.
Multicast: One sender transmits to a set of peers, which are known.
Similar to Publish-Subscribe
Other concepts: Anycast, Convergecast, Geocast…